42 HISTORY OF ELECTRICITY. 



doing so, by one of Newton's "Rules of Philoso- 

 phizing," in which he directs the philosopher to 

 assume, in his theories, "causes which are true." 

 The usual interpretation of a "vera causa," has 

 been, that it implies causes which, independently of 

 theoretical calculations, are known to exist by their 

 mechanical effects ; as gravity was familiarly known 

 to exist on the earth, before it was extended to 

 the heavens. The electric fluid might seem to be 

 such a vera causa. 



To this I should venture to reply, that this 

 reasoning shows how delusive the Newtonian rule, 

 so interpreted, may be. For a moment's considera- 

 tion will satisfy us that none of the circumstances, 

 above adduced, can really prove material currents, 

 rather than vibrations, or other modes of agency. 

 The spark and shock are quite insufficient to sup- 

 ply such a proof. Sound is vibrations, light is 

 vibrations; vibrations may affect our nerves, and 

 may rend a body, as when glasses are broken by 

 sounds. Therefore all these supposed indications 

 of the reality of the electric fluid are utterly fal- 

 lacious. In truth, this mode of applying Newton's 

 rule consists in elevating our first rude and un- 

 scientific impressions into a supremacy over the 

 results of calculation, generalization, and systematic 

 induction 17 . 



17 On the subject of this Newtonian Rule of Philosophizing, 

 see further Phil. 2nd. Sc. B. xii. c. 13. I have given an account 

 of the history and evidence of the Theory of Electricity hi the 



